1. Field of the Invention
This invention relates generally to the printing of moving webs and is concerned in particular with water-based foamable ink printing composition and a method of making the same.
2. Description of the Prior Art
The invention is especially useful in, although not limited to, the rotogravure printing of paper webs. Since its inception in the late 1800's, rotogravure printing has been carried out primarily with solvent based inks. The solvents are toxic and highly flammable, and consequently printing plant personnel are exposed continuously to potentially serious health, fire and explosion hazards. As a result, in spite of the implementation of elaborate and expensive protective measures such as for example solvent recovery and air pollution abatement systems, electrically grounded presses, shielded electric motors, etc., insurance costs remain extremely high. Moreover, because solvents are extracted from petroleum, their costs have increased dramatically during the last decade, as has the cost of the energy consumed by the dryers required to dry solvent inks after printing.
It has been suggested to coat or print a web of cloth, paper or the like with a water-based foamed ink. U.S. Pat. No. 2,971,458, Kumins, is believed to be the most relevant prior art. This reference teaches the foaming of water-based inks by conventional foaming devices such as mechanical mixers, followed by transfer of the foamed ink into the cells of a gravure cylinder and subsequent transfer of the foamed ink from the cells of the cylinder to a web to be printed. Further in this reference, the disclosed compositions include additives to enhance stability, but no additive is taught which is used both to enhance the mixing of the composition during foaming and to control the fluidity and stability of the ink once foamed.
Although this reference suggests the use of a water-based foamed ink for the printing of a moving web of paper, there presently is no economically successful commercial implementation of this suggestion.